For Emma Macorison, pulling a muscle in a kickboxing class was par for the course.

The 34-year-old London-based publicist was used to the odd injury, having done the sport for more than five years.

So when she hurt her leg in July, she didn’t give it much thought.

Little did she know that this time
was very different.

Within weeks, she would be admitted to hospital with
a life-threatening blood clot on the lung — caused by a DVT (deep vein
thrombosis, a blood clot in the leg).

The initial injury had seemed innocuous, Emma recalls.

‘I was warming up with my instructor, doing some sparring and kicking
the pads he was holding, when I suddenly felt a sharp pain in my right
calf muscle.

‘It felt
like someone had thrown a stone into my calf.

'I just thought: “Oh no,
I’ve pulled a muscle.”

'Everyone who goes to kickboxing classes knows you
can get minor injuries like this, so I wasn’t too worried.

‘After
a few minutes, I tried to stand on my right leg, but it was far too
painful, so eventually I hobbled out of the class, into a taxi and home —
my neighbour had to help me up the stairs to my second-floor flat.’

The next day, Emma limped into work, hopping with just the toe of her affected leg on the ground to protect it.

Two days after the injury, she noticed her leg felt a bit tingly and the calf muscle was hot to the touch.

‘It also looked a bit puffy just above the ankle,’ she recalls.

‘I’m not a wimp with pain, and I just thought, “Well, it will get better eventually,” so I took ibuprofen and paracetamol, and carried on with life as best as I could.’

But four days later, Emma woke with a sickening pain in her right side near her ribs, which made breathing difficult.

She also started coughing.

Nearly three months after the original injury, Emma is still suffering from fatigue and has to wear a compression stocking on her leg to help the circulation

‘I’d no idea what was wrong, but the pain was excruciating.

'I felt panicky because every time I tried to breathe it hurt so much.

‘I was on my own, and as the day wore on, I started coughing up blood. I rang NHS Direct in the afternoon, and an ambulance was sent to take me to hospital.’

At St Thomas’s Hospital, Central London, Emma had an X-ray and was wrongly told she had a broken rib.

‘I took the bus home and resigned myself to a week off work.

‘I’d also asked them to look at my leg while I was there, so they gave me some crutches.

‘The next day, I rang my local surgery to ask for stronger painkillers, as ibuprofen just wasn’t working.

'I can't go kickboxing until I am fitter...but I'd go back in a flash if I could, although I am worried about developing post-thrombotic syndrome,' said Emma

‘If you sit still for more than 90 minutes, blood flow through your veins drops by 50 per cent.

'And when you’re ill your blood gets sticky — so is more likely to clot.’

Women on hormonal treatments, such as HRT or the Pill, are at greater risk.

So, too, are pregnant women or patients with an acute illness such as cancer.

Another risk factor is damaging a vein in an accident, or having surgery (especially on hips and knees). In fact, while the popular perception is that DVTs are caused mainly by long-haul flights, most occur following an operation.

Other risk factors include being over the age of 40, being treated for heart failure or circulation problems, or a family history of the problem.

Many people don’t realise that a number of simultaneously occurring yet apparently innocuous things can cause DVT.

‘DVT is often caused by a combination of risk factors,’ explains Professor Hunt.

‘So it might be that someone gets the flu, is taking the Pill, and then goes on a long-haul flight — the three things add up to create a problem.’

In Emma’s case the probable triggers included getting pregnant, and then in July having the pregnancy terminated when it was discovered the foetus had a genetic abnormality, Trisomy 13 – ‘which would have almost certainly killed the baby before or soon after the birth'.

Pregnancy in general is a risk factor for increasing blood stickiness - and continues for up to 12 weeks after the end of one.

In an attempt to take her mind off the sadness of her loss and lose some weight, Emma had returned to her local kickboxing class, causing the torn muscle. The injury may have been the third factor, says Dr Hunt, although no one can be sure.

Not being as active was the final key in the DVT puzzle.

But despite her GP’s warning, Emma didn’t go straight to hospital, but home to watch the Olympics with a friend.

‘That was a mistake, but I’d been alone all week and didn’t want to let my friend down,’ explains Emma.

She finally got the bus to St Thomas’s at 10.30pm.

‘At 2am, I had blood tests to find out if I had any clots and they came back as positive.’

Not only that, one of her lungs had partially collapsed and she was immediately admitted to hospital.

‘It was a huge shock — I just thought I had a broken rib, and suddenly to find out I was very ill, and could die without immediate treatment to dispel the clots, was very upsetting.’

Emma spent a week in hospital, with daily injections of heparin and warfarin, drugs that make the blood less sticky.

Currently patients on warfarin must attend regular anti-coagulant clinics to monitor their blood.

However, there is now a new, less complex treatment for DVT, a drug called rivaroxaban.

The drug, which was approved for use on the NHS in July, reduces blood stickiness uniformly. It isn’t affected by diet, so patients won’t need to attend monitoring clinics.